The labral gland in termites: evolution and function

Termites are important contributors to ecosystem functioning. They are highly abundant in tropical and sub-tropical habitats, and represent an important resource for a wide range of predators. Their evolutionary success is driven largely by a life in populous colonies with a complex communication system controlled by a rich set of exocrine glands whose secretions are involved in many aspects of termite life. As many as 20 different exocrine organs are known to occur in termites. Among them, the labral gland has been largely understudied. Here we examine the structure of the labral gland in workers of 28 species and imagoes of 33 species across all termite taxa, and in the Cryptocercus wood roach. The labral gland is present in all species, and comprises two secretory regions located on the ventral side of the labrum and the dorso-apical part of the hypopharynx, respectively. The epithelium of the gland consists of class 1 secretory cells with an abundance of smooth endoplasmic reticulum, and long microvilli with a channel inside, which releases secretion through a modified cuticle. Our observations suggest that the labral gland is involved in defensive communication after encounter with a non-nestmate.